In the heretofore known effluent oil collecting vessel of twin-hull type, effluent oil collecting means is provided between the opposite hulls of the twin-hull, and while the vessel is advancing, effluent oil flowing into the water surface area between the opposite hulls is collected. The effluent oil suction means are roughly classified into four types, that is, a vortex type in which oil is collected to the center by making use of a vortex; a rotary belt type in which oil is forcibly conveyed together with the sea water into a tank by making use of an inclined rotary belt; a rotary drum type in which blades are fixedly secured to a drum and oil is taken in by rotating the drum; and a natural inflow type in which the water line is utilized, and while navigating, floating oil is taken into a tank by making use of a weir or an inclined plate. However, these effluent oil suction means which have been heretofore used and which are of fixed type, would follow pitching and rolling motions of a vessel and would move jointly with the hull of the vessel, and thus since the suction means cannot follow the waves, an oil collecting efficiency under a waved condition is bad.
Also, when the suction means is made to float by means of a float and is hung with a rope, an opening portion sinks into waves or floats up above the water surface, and the oil collection efficiency is lowered. In addition, dusts or seaweeds are liable to adhere to an oil intake port together with oil, resulting in blocking of the oil intake port, and when the adhesion becomes very high due to the high viscosity of the effluent oil, cleaning must be performed frequently. Still further, there are inconveniences and disadvantages when the oil is dispersed by tides; winds and waves, then it took considerable time to collect the oil. Also, if the oil layer is thin, then a large amount of sea water is sucked, resulting in reduction of the oil collection efficiency.